Gas ranges typically use atmospheric burners. Such atmospheric burners perform well when a plentiful supply of secondary air surrounds the burner. Typically, secondary air is supplied in such ranges through one or more aeration openings in the burner pan surrounding the burner body. In addition, secondary air is often supplied through a central opening in the burner. Such openings, however, create problems in the use of gas ranges because they permit spills, boilovers and the like to run from the top of the gas range into its interior, creating an undesirable cleaning problem.
Furthermore, combustion of any fuel, including natural gas and the other gas fuels that are used in household gas ranges, generally results in undesirable byproducts such as carbon monoxide (CO) and oxides of nitrogen (NO.sub.x). These pollutants are not direct products of perfect combustion but generally result from incomplete combustion and the presence of secondary air. Efforts to protect the environment have resulted in legislation and standards to limit permissible levels of such pollutants in both the United States and Europe, and it is expected that such legislation will become more widespread and that the resulting standards will become more stringent. It is clearly desirable to avoid the generation and distribution of such pollutants during the operation of gas ranges in the household of a user, and various apparatus have been proposed to reduce the generation and distribution of pollutants in the operation of gas burners.
As indicated above, it is desirable that the range top be sealed to preclude liquids and materials from entering the interior of the range. Some sealed, smooth-top gas ranges have included blowers or fans to produce both a flow of combustion air to, and an exhaust of combustion products from, burners that are located under a sealed glass or ceramic top of the range. See U.S. Pat. Nos. 2,870,829; 3,404,350; 3,870,457; 3,968,785; and 4,020,821. For example, U.S. Pat. No. 4,020,821 to Reid, Jr. et al, discloses a gas burning range with a sealed, smooth, glass or ceramic top lying over a plurality of infrared burners. In the gas range of Reid, Jr. et al., a primary gas/air mixture is provided for each burner from a combined gas and air shutter valve to a burner tip for combustion. A blower creates a negative pressure in each burner and throughout the flow path for the fuel gas, draws a flow of additional air for combustion into the gas flow path, and creates an exhaust for the combustion products leaving the burners. Such sealed top ranges generally rely on infrared heating of cooking utensils through the sealed top and are thus not as thermally efficient or as fast as open flame ranges.
Sealed top gas ranges with open flame burners have been obtained by, for example, sealing the burner head to the top range surface or burner pan. The use of such "sealed burners" in gas range construction eliminates the openings through which secondary air reaches the burners, and the air needed for combustion must enter the combustion zone in a path which is below the existing products of combustion, and the performance of the range burners is vulnerable to a number of adverse effects. Among the problems presented by such open flame, sealed burner constructions are the recirculation of products of combustion, the tendency of the gas flames to "reach" for combustion air which distorts the flame pattern and detracts from even heat distribution, the destruction of flame patterns as a result of adjacent walls that interfere or divert the secondary air supply, and flame distortion created by the simultaneous operation of adjacent burners that compete for secondary air as their flames tend to be drawn toward the natural thermal updraft of the adjacent burners. Attempts to solve such problems have included high grate tops and other barriers seeking to prevent such burner interaction.
Gas ranges with downdraft exhaust systems are known, as shown, for example, by U.S. Pat. Nos. 4,413,610; 4,413,611; 4,409,954; 4,457,293; and 4,750,450.
The problems attendant sealed burners are compounded in gas ranges with downdraft exhausts. The purpose of the downdraft exhaust is, of course, to remove products of combustion and cooking vapors from the gas range during its operation by creating a flow of exhaust air across the top of the range adjacent the burners. The air flow from such a forced exhaust pulls the flames in the direction of the exhaust, interfering with proper combustion and heat distribution at the burners. The air flow created by the downdraft exhaust means also pulls the secondary air away from the burner flames, and the disturbed flame cones impinge on relatively cold grate fingers to cause incomplete combustion. In some designs, heat from the burners of a downdraft gas range has been so unevenly distributed that it is not possible to evenly cook such foodstuffs as pancakes, eggs and sausages in a large skillet. In addition, a low simmer flame cannot be satisfactorily stabilized and ignition of the flame becomes unreliable.
Prior efforts to combine open flame sealed burners with a downdraft exhaust have also used shields extending several inches above the burner to help protect the burner flame from the exhaust flow. Other attempts have elevated the entrance to the downdraft exhaust plenum several inches above the cooktop in an effort to minimize the adverse effect of the exhaust at the cooktop surface. In still further efforts, the downdraft exhaust has been reduced in power, or the entrance to the downdraft plenum has been remotely located from the burners, or has been reduced in intake area, in attempts to minimize the adverse effect of the exhaust. Each of these methods, however, detracts from the effectiveness of the downdraft exhaust and reduces its ability to capture and remove cooking vapors, odors, heat and other products of combustion and cooking.
The use of powered gas burners in gas cooking ranges has been disclosed in the art. For example, U.S. Pat. No. 3,468,298 to Teague, Jr. et al. discloses a sealed, smooth-top gas range with a plurality of powered infrared burners. In the gas range of Teague, Jr. et al, a blower supplies air to and pressurizes a manifold extending along the front of the range. The manifold has openings formed in its bottom, one for each of the plurality of burners. A slide valve for each burner includes air control orifices cooperating with a manifold opening for each burner to permit a variable and controllable flow of combustion air from the manifold into a separate valve manifold, and from the separate valve manifold through a venturi mixer to its associated burner. Gas flow to the venturi mixer and burner is controlled by a diaphragm-operated gas flow regulator, which is operated by the air pressure in the valve manifold to control the gas/air mixture to each burner.
U.S. Pat. No. 4,569,328 to Shukla et al. seeks to avoid emission of air pollutants, such as carbon monoxide and oxides of nitrogen, into the kitchen. The Shukla et al. patent discloses a gas range with a ceramic tile forming a plurality of openings provided, preferably, with a forced air-gas mixture and adapted to provide an open standing flame close to its upper surface so that the ceramic tile burner will provide high radiant heat as a result of the gas flame. In Shukla et al.'s invention, a jet plate is positioned between the infrared burner and the supporting surface for the cooking utensil. The jet plate is stated to be of considerable importance in the achievement of high thermal efficiencies. Shukla et al.'s jet plate includes a plurality of perforations or jet holes to form high velocity gas jets from the combustion products of the infrared burner, and the gas jets are directed to impinge against and convectively heat the lower surface of the cooking utensil and then pass into the atmosphere of the kitchen above the cooktop.
While Shukla et al. discloses that his ceramic tile may operate as an atmospheric burner, in Shukla et al.'s preferred embodiment, a blower is positioned in the central portion of the range to pressurize an air plenum, which is linked to a plurality of mixing valve assemblies to control the flow of the forced air-gas mixture to the plurality of burners. Each mixing valve assembly provides a selected stoichoimetry for its associated burner by mechanically coupling a rotatable air orifice plate to a gas valve shaft so that by rotation of the gas valve shaft to control gas flow, air flow is simultaneously controlled by the alignment of one or more of several discrete openings in the air orifice plate with a fixed opening in an air flow tube.
U.S. Pat. No. 4,960,377 to Nunes et al. discloses a gas-air mixing valve for use with residential and commercial cooking ranges. The Nunes et al. valve is designed for use preferably in a gas range having a plurality of gas burners. The Nunes et al. valve is attached to an air plenum which is pressurized by an air blower. The Nunes et al. valve is adapted to be mounted over a hole formed in the air plenum and to provide two valve openings communicating with the interior of the air plenum, one of the valve openings forming an inlet to an air-gas mixing chamber within the valve, and the other valve opening communicating with atmosphere. The two valve openings to the pressurized air plenum formed by the Nunes et al. valve are covered by a rotating orifice plate. The rotating orifice plate includes an opening cooperating with the opening between the air plenum and the air-gas mixing chamber, and an opening cooperating with the opening to atmosphere so that as the size of the entrance to the air-gas mixing chamber is increased by rotation of the orifice plate, the size of the opening between the air plenum and atmosphere is correspondingly decreased to maintain a constant air flow in the plenum for the operation of each of the gas burners. As the orifice plate is rotated, the gas valve is also operated to maintain a selected forced air-gas mixture to each cooking burner.
Other arrangements of gas ranges with power burners, and air/gas control valves for gas ranges with power burners are disclosed in U.S. Pat. Nos. 3,162,237; 3,169,871; 3,371,699; 3,592,180; 4,622,946; and 4,794,907. Notwithstanding these various developments, the use of powered surface burners is rare in household gas ranges. Variations in the characteristics and burning properties of gas from utility to utility and locale to locale have made it difficult to achieve reliable and repeatable combustion characteristics with powered surface burners in a household range.
Other patents disclosing sealed burners include British Pat. Nos. 1,443,553; and 1,543,618; and U.S. Pat. Nos. 4,518,346; 4,565,523; 4,570,610; 4,690,636; 4,757,801; 4,773,383; 4,971,024; and 5,046,477.
Notwithstanding the efforts of others, no one, prior to this invention has provided a dual mode gas range with the combined advantages and abilities of a sealed top construction, downdraft exhaust and open flame gas burners that are operable with a powered gas/air mixture with a downdraft exhaust, and otherwise as an atmospheric range.